Adaptive differences in digestive enzyme activity in the crab Neohelice granulata in relation to sex and habitat

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Neohelice granulata (Dana, 1851) is a semi-terrestrial burrowing crab that inhabits estuaries and saltmarshes feeding on grasses or sediment depending on the microhabitat they occupy (vegetated saltmarsh or bare mudflat). Specific cellulolytic, amylolytic, and proteolytic enzyme activities were analyzed in midgut gland homogenates of males and females from each microhabitat fed in the laboratory with Spartina densiflora leaves and sediment, respectively, in order to detect sex, food and microhabitat related differences. The presence of β-1,4-glucosidase, endo-β-1,4-glucanase, α amylase, trypsin and chymotrypsin were confirmed. Specific cellulolytic activity was higher in crabs fed on leaves than in those fed on sediment or in no fed controls and variable differences between sexes were observed. Specific amylase activity of crabs fed on leaves was the lowest recorded. Trypsin and chymotrypsin specific activities were higher in saltmarsh crabs fed on leaves than in mudflat crabs fed on sediment. Different mechanisms of enzyme regulation to explain the observed differences among groups were suggested. Additionally, differences between sexes suggest different metabolic needs related to gonad maturation. It is concluded that N. granulata has the ability to adapt digestive enzyme production to support its physiological and metabolic needs based on the different food sources available at each microhabitat.

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